A bis-phenanthridinium salt that we have recently synthesized and studied has been shown to doubly intercalate in helical DNA with very high binding affinity. However, its low solubility in aqueous solutions and poor ability to inhibit nucleic acid synthesis in cultured cells suggests modifications in structure. We plan to synthesize several double intercalators with other chain linking the 6-phenyl substituents of two phenanthridinium moieties. Although molecular models suggest that the meta position of the 6-phenyl group is the most advantageous site, at least sterically, for this linkage, we propose the preparation of compounds in which the linkage is through the para positions, as well as through the meta. Study of the complexes of these drugs with DNA should give data leading to better understanding of relative interactions of these isomeric compounds with DNA. Such studies include biophysical and spectral measurements as well as biochemical assays.